1. Field of the Invention
Example embodiments of the present invention relate to a length measurement method and apparatus, and more particularly, to a method of measuring a critical dimension (CD) of a semiconductor device and a related apparatus.
2. Description of Related Art
A conventional method of manufacturing a semiconductor device may include processes of forming a thin layer on a semiconductor substrate and partially removing the thin layer to form a pattern. The pattern may have a dimension and an interval designed according to characteristics of the semiconductor device. Therefore, it may be very important to confirm the dimension and interval of the pattern. A critical dimension (CD) may be defined as a width or an interval of the smallest pattern.
Conventionally, a scanning electron microscope. (SEM) is widely used to measure the CD of a semiconductor device, for example. The SEM may irradiate a position on a semiconductor substrate with an electron beam, and may detect a secondary electron emitted from the semiconductor substrate to obtain image data of the semiconductor substrate. The width and/or interval of a pattern on a substrate may be measured using the image data.
FIG. 1 is a plan view showing a conventional method of measuring a CD using a SEM, and FIG. 2 is a diagram showing a waveform detected by the SEM along a scan line S1 of FIG. 1.
Referring to FIG. 1, a semiconductor substrate may be inserted into a SEM. The semiconductor substrate may include a line pattern 10, and image data 5 of the line pattern 10 may be obtained. The image data 5 may include a first side 11 and a second side 12 of the line pattern 10. A measurement window 20 may overlay and extend across the first side 11 and the second side 12. The measurement window 20 may be set to have a length L1 and a width W1.
Referring to FIG. 2, the waveform detected by the SEM may be displayed as curves 30 to 35. That is, the waveform detected by the SEM along the scan line S1 of FIG. 1 may include a primary horizontal line 30, a secondary horizontal line 35, a first inflection point 31 and a second inflection point 32. The secondary horizontal line 35 may be displayed and correspond to the line pattern 10; the first inflection point 31 may be displayed and correspond to the first side 11; and the second inflection point 32 may be displayed and correspond to the second side 12. A CD value CD1 between the first side 11 and the second side 12 may be measured by calculating a distance between the first inflection point 31 and the second inflection point 32.
However, the first side 11 and the second side 12 may have rough surfaces due to, for example, machining errors that may occur during the manufacturing process. The CD value CD1 measured along the scan line S1 may have an average width and error of the line pattern 10. To address errors, it may be advantageous to adopt an average value of CD values obtained by repeatedly measuring the CD at various positions within the width W1 while moving the scan line S1 in a direction parallel with the width W1 of the measurement window 20. Therefore, as the width W1 of the measurement window 20 increases, the measurement accuracy may increase. In addition, the length L1 of the measurement window 20 should be longer than a distance between the first side 11 and the second side 12.
As shown in FIG. 1, when the first side 11 and the second side 12 are parallel and symmetrical to each other, the width W1 of the measurement window 20 may be set to a dimension, which may provide sufficient measurement accuracy. That is, it may be possible to increase the measurement accuracy by increasing the width of the measurement window. However, patterns having symmetrical and asymmetrical structures may be formed in a semiconductor substrate. When the first side 11 and the second side 12 have an asymmetrical structure, it may be difficult to set the width W1 of the measurement window 20 to a dimension, which provides sufficient measurement accuracy. Therefore, the measurement accuracy obtained with a convention measurement method may be insufficient.
A semiconductor device employing structures providing remarkably increased integration efficiency, e.g., oblique patterns, is being researched. It is difficult to set the measurement window having a dimension capable of obtaining sufficient measurement accuracy using conventional measurement methods.